The invention relates to magnetic recording heads, and more particularly, to a permanent magnet for generating a magnetic bias field in a read head of such recording heads.
Devices utilizing the giant magnetoresistance (GMR) effect have utility as magnetic sensors, especially as read sensors in read heads used in magnetic disc storage systems. The GMR effect is observed in thin, electrically conductive multi-layer systems having magnetic layers. In operation, a sense current is passed through the read head of the magnetic disc storage system. The presence of a magnetic field in the storage media adjacent to the sensor changes the resistance of the sensor. A resulting change in voltage drop across the sensor due to the change of the resistance of the sensor results in an output voltage that can be measured and used to recover magnetically stored information.
The output voltage is affected by various characteristics of the sensor. The sense current can flow through the sensor in a direction that is perpendicular to the planes of the layers or stack strips that comprise the sensor, i.e. current-perpendicular-to-plane component or CPP, or the sense current can flow through the sensor in a direction that is parallel to the planes of the layers or stack strips, i.e. current-in-plane or CIP. The CPP operating mode can result in higher output voltage than the CIP operating mode. The higher the output voltage, the greater the precision and sensitivity of the read head sensor in sensing magnetic fields from the magnetic medium. Therefore, it is desirable to maximize the output voltage of the read head and specifically the sensor thereof.
A read head for use in a disc drive can include a first lead/shield, a second lead/shield, and a GMR sensor, or also referred to as a read sensor or a GMR stack, located between the first lead/shield and the second lead/shield. For operation of the sensor, a sense current is caused to flow through the read head and particularly through the sensor. As resistance of the sensor changes, the voltage across the sensor changes. This is used to produce the output voltage.
The CPP-GMR has been shown to potentially have a larger GMR than CIP sensors because all of the current needs to pass through every ferromagnetic/non-magnetic/ferromagnetic (FM/NM/FM) series of interfaces and none of the current is shunted around the interfaces. Since every film and interface leads to additional resistance, it is desired to have all the films and interfaces contribute to the overall change in resistance. One such sensor is a GMR multilayer, which consists of a series of FM/NM bilayers. Every series of interfaces is an opportunity for interfacial spin dependent scattering and every FM material is an opportunity for bulk spin dependent bulk.
For a CPP type sensor, the sensor may be magnetically biased to reduce noise in the read signal and improve the linearity and gain of flux sensing. The magnetic biasing may be achieved by placing a permanent magnet adjacent the sensor such that the magnetization of adjacent ferromagnetic layers of the sensor is 90xc2x0 with respect to each other. More specifically, this may be achieved by placing a permanent magnet having a magnetization in a direction that is normal to an air-bearing surface of a read sensor such that the magnetization of the adjacent ferromagnetic layers that make up the read sensor are biased by the permanent magnet, and specifically by the magnetic bias field, to a different position.
When using a permanent magnet to bias a read sensor, it is important that the sensor is biased properly. If the sensor is, for example, either over or under biased, the signal will become non-linear and create a loss of amplitude, signal asymmetry and detection and tracking problems. One difficult aspect of properly biasing a sensor is that the actual bias point cannot be exactly determined until after almost the entire read head is built. If the bias point is not correct and there is no way of adjusting the bias, the read head may not be usable.
There is identified a need for an adjustable permanent magnet bias for magnetically biasing a read sensor.
The invention meets the identified need, as well as other needs, as will be more fully understood following a review of this specification and drawings.
In accordance with an aspect of the invention, a current perpendicular to the plane read head comprises a read sensor having an air-bearing surface and an opposing top surface and a permanent magnet positioned adjacent the top surface of the read sensor. The permanent magnet generates a magnetic bias field in the read sensor such that the biasing of the read sensor causes the change in resistance to operate in a more linear fashion making the change in resistance of the sensor and the resulting change in voltage drop across the sensor easier to measure. The permanent magnet has a magnetization in a direction other than normal to the air-bearing surface of the read sensor. The specific direction of magnetization of the permanent magnet is selected according to the desired amount of magnetic bias field to be generated in the read sensor.
In accordance with another aspect of the invention, a current perpendicular to the plane read head comprises a read sensor and means for generating and adjusting a magnetic bias field in the read sensor.
In accordance with yet another aspect of the invention, a read head for a magnetic disc storage system comprises a read sensor having an air-bearing surface and a permanent magnet positioned adjacent the read sensor for magnetically biasing the read sensor. The permanent magnet has a magnetization set in a direction other normal to the air-bearing surface of the read sensor. The direction of magnetization in the permanent magnet has a direct relationship to the strength of the magnetic field that biases the read sensor.
In accordance with a further aspect of the invention, a magnetic disc drive storage system comprises a housing, a rotatable magnetic storage medium positioned in the housing, and a movable recording head mounted in the housing adjacent the magnetic storage medium. The recording head includes a current perpendicular to the plane read head. The current perpendicular to the plane read head comprises a read sensor having an air-bearing surface and an opposing top surface and a permanent magnet positioned adjacent the top surface of the read sensor for generating a magnetic bias field in the read sensor. The permanent magnet has a magnetization in a direction other than normal to the air-bearing surface of the read sensor.
In accordance with an additional aspect of the invention, a method of using a permanent magnet to generate a magnetic bias field in a read sensor having an air-bearing surface and an opposing top surface comprises establishing a magnetization in the permanent magnet, and positioning the permanent adjacent the top surface of the read sensor such that the magnetization of the permanent magnet is in a direction other than normal to the air-bearing surface of the read sensor. The method may also include adjusting the magnetization direction of the permanent magnet to adjust the strength of the magnetic bias field generated in the read sensor. The direction of magnetization of the permanent magnet may be pre-determined according to the desired amount of magnetic bias field to be generated in the read sensor. The permanent magnet bias can be adjusted after, for example, quasi-static testing or dynamic (spin-stand) testing to determine the optimum bias conditions for reading back data.